The effect of different photoperiods: 24 h illumination and a 12:12-h light/dark (12L:12D) cycle on the growth rate and biomass productivity was studied in five algal species: Neochloris conjuncta, Neochloris terrestris, Neochloris texensis, Botryococcus braunii and Scenedesmus obliquus. The green microalgae examined differ in the reproduction mode. Continuous illumination stimulated the growth of B. braunii and S. obliquus more effectively than the growth of the microalgal species from the genus Neochloris. However, under shorter duration of light of the same intensity (12L:12D cycle), the growth of all the three species of Neochloris was stimulated. Under continuous illumination, the specific growth rate in the first phase of B. braunii and S. obliquus cultures was higher than the growth rate of Neochloris, whereas under the 12L:12D cycle, the specific growth rate of all the three Neochloris species was generally higher than that in B. braunii and S. obliquus. As a result, the light regime influenced algal biomass productivity differently. The maximum biomass productivity was obtained in B. braunii and S. obliquus cultures carried out at continuous illumination. All the Neochloris species produced biomass more efficiently at the 12L:12D cycle, which was two–threefold higher than that of B. braunii and S. obliquus. The unicellular species of the green microalgae from the genus Neochloris, examined for the first time in this study, are promising prospective objects for algal biotechnology.

Microalgae are natural resources of intracellular compounds with a wide spectrum of applications in, e.g., the food industry, pharmacy, and biofuel production. The extracellular polymeric substances (EPS) released by microalgal cells are a valuable bioproduct. Polysaccharides, protein, lipids, and DNA are the main constituents of EPS. This review presents the recent advances in the field of the determinants of the synthesis of extracellular polymeric substances by microalgal cells and the EPS structure. Physical and chemical culture conditions have been analyzed to achieve useful insights into the development of a strategy optimizing EPS production by microalgal cells. The application of microalgal EPS for flocculation and mechanisms involved in this process are also discussed in terms of biomass harvesting. Additionally, the ability of EPS to remove toxic heavy metals has been analyzed. With their flocculation and sorption properties, microalgal EPS are a promising bioproduct that can potentially be used in harvesting algal biomass and wastewater management.

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The prospect of depletion of natural energy resources on the Earth forces researchers to seek and explore new and alternative energy sources. Biomass is a composite resource that can be used in many ways leading to diversity of products. Therefore, microalgal biomass offers great potential. The main aim of this study is to find the best physical method of microalgal biomass pretreatment that guarantees efficient lipid extraction. These studies identifies biochemical composition of microalgal biomass as source for biodisel production. The influence of drying at different temperatures and lyophilization was investigated. In addition, wet and untreated biomass was examined. Cell disruption (sonication and microwave) techniques were used to improve lipid extraction from wet biomass. Additionally, two different extraction methods were carried out to select the best method of crude oil extraction. The results of this study show that wet biomass after sonication is the most suitable for extraction. The fatty acid composition of microalgal biomass includes linoleic acid (C18:2), palmitic acid (C16:0), oleic acid (C18:1), linolenic acid (C18:3), and stearic acid (C18:0), which play a key role in biodiesel production.

In recent years, researchers have highlighted the role of low cost-efficient agro-industrial by-products used as supplements in algal culture media. The aim of the study was to identify and characterize the basic metabolic pathways in Tetradesmus obliquus cells induced by supplementation with beet molasses in photoheterotrophic and mixotrophic culture conditions. to assess the impact of the nutritional strategy in unicellular algae, growth curves were plotted and lipid, carbohydrate, and protein levels were determined. Fourier Transform Infrared Spectroscopy was applied to measure the Tetradesmus obliquus cell composition. Additionally, the C16-C18 fatty acid profile of Tetradesmus obliquus was determined by gas chromatograph/mass spectrometry. The switch from autotrophy to photoheterotrophy and mixotrophy contributes to shortening of the adaptation growth phase. The highest protein content was obtained in the mixotrophic growth. This study has demonstrated high content of 18:1, cisΔ 9 , 18:2, cisΔ 9,12 , ω6, and 18:3, cisΔ 9,12,15 , ω3 in photoheterotrophic and mixotrophic culture conditions. High levels of proteins and essential fatty acids make Tetradesmus obliquus cell biomass important for human and animals health. Microalgae are not only a source of many valuable bio-products e.g. proteins, carbohydrates, lipids, ω3 and ω6 fatty acids or pigments applied in many different commercial sectors but can be a simple and economical solution to wastewater treatment and waste management 1. Algal cells utilize effectively agricultural, industrial and municipal wastewaters, waste raw materials, and by-products from many branches of industry. Algae are capable of assimilating organic compounds and other ingredients for biomass production and synthesis of both basic and specific metabolites. Additionally, the use of wastewaters and waste materials make microalgal biomass and bio-product production environmentally friendly 2. A number of studies have described supplementation of the algal culture medium with agricultural waste such as dairy manure 3 , liquid waste produced in piggeries 4 , post-fermentation effluents and wastewater from fruit, vegetable or cultivated plant processing, i.e. residues of cane bagasse and pineapple peel 5 , cassava 6 , sweet sorghum 7 , or hydrolysate of Jerusalem artichoke tubers 8. Most algae are autotrophs; however, some species such as Auxenochlorella protothecoides 9 Parachlorella kessleri 10 and Tetradesmus obliquus can assimilate organic compounds. Cultivation modes based on organic carbon sources include heterotrophy, photoheterotrophy, and mixotrophy 11. Compared to the heterotrophic mode, the photoheterotrophic and mixotrophic cultivation systems have several advantages e.g. intensification of algal growth and synthesis of valuable metabolites, such as fatty acids 12. Green algae growing in photoheterotrophic and mixotrophic culture conditions are natural producers of polyunsaturated fatty acids 10,13. In terms of human nutrition, one of the most important PUFAs are essential fatty...

The aim of this study was to determine the suitability of beet molasses, an agro-industrial by-product, as an alternative culture medium component for photoheterotrophic and mixotrophic cultivation of Parachlorella kessleri. Application of beet molasses improved microalgal cell growth and modified the biochemical composition of P. kessleri biomass. During the addition of molasses to culture media with simultaneous aeration, the maximum biomass productivity, oil and protein productivity, and calorific value were 0.42 g L−1 day−1, 112.56 and 244.95 mg L−1 day−1, and 22.1 MJ kg−1, respectively. Under these conditions, the total content of polyunsaturated C16-C18 fatty acids decreased, which was suitable for application in biodiesel. Besides oils and carbohydrates, P. kessleri had an ability to synthesize significant amounts of proteins, especially during molasses utilization. This provides a possibility of a wide range of non-fuel applications of P. kessleri biomass.

This paper analyses the suitability of common goldenrod plants as monoand co-substrates for biogas production. Furthermore, the role of bioactive compounds included in the biomass of this plant species was investigated. The results showed that the common goldenrod species produced lower biogas and methane yields than maize silage. However, the methane fermentation of their mixture resulted in approximately 9.5% higher biogas yield and 16.6% higher methane yield compared to the theoretical yields estimated based on two mono-digestions. A statistically significant increase in biogas production efficiency resulted from more favorable C/N ratio and the influence of bioactive compounds contained in common goldenrod. The addition of goldenrod crude extract caused an approximately 30% increase in the biogas yield of maize silage. This effect may be associated with a positive impact of biologically active substances on microorganisms or with a decrease in redox potential of the fermenting mass.

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